1. Field of the Invention
The present invention relates to a playback data detecting apparatus such as a digital disk storage device (an optical disk storage device, a magneto-optical disk storage device, a phase-change disk storage device, a hard disk device, etc.), a digital VCR and the like.
2. Description of the Prior Art
Conventionally, digital-recording disk devices, digital-recording VTRs and the like have recorded data by converting the data into recording codes without recording the data as it is. As representative recording codes, there are a 1-7 code and a 2-7 code.
FIG. 10 shows a code conversion table of the 1-7 code. In FIG. 10, 2 data bits or 4 data bits are recorded after being converted into 3 channel bits or 6 channel bits, respectively, according to an NRZI rule. The NRZI rule is a rule to invert a data bit and record the same when it is "1" while to record a data bit as it is when it is "0". A remarkable feature of the 1-7 code is that there are one to seven "0"s between "1" and "1" after conversion according to the table in FIG. 10.
FIG. 11 shows a code conversion table of the 2-7 code. In FIG. 11, 2 data bits, 3 data bits or 4 data bits are recorded after being converted into 4 channel bits, 6 channel bits or 8 channel bits respectively according to the NRZI rule. A remarkable feature of the 2-7 code is that there are two to seven "0"s between "1" and "1" after conversion according to the table in FIG. 11.
Further, both codes comprise synchronizing signals inserted therein every several hundred or thousand bits for recovering from a decoding pattern shift which likely occurs due to an error at the time of recording or playback. The synchronizing signals employ channel bit patterns which do not appear in ordinary data to be clearly distinguished therefrom.
Whereas recently, there is proposed a method of correcting bit errors for a recording code having limited continuous bit length patterns such as the 1-7 and the 2-7 code by way of Viterbi decoding. For example, a method of performing the Viterbi decoding by subjecting a recorded code having a minimum non-inverted interval of 2-channel bits such as the 1-7 code to ternary detection and a method of performing the Viterbi decoding by subjecting a recorded code having a minimum non-inverted interval of 2-channel bits such as the 1-7 code to binary detection are described in the Japanese Unexamined Patent Publication Nos. 4-307817(1992) and 4-298865(1992), respectively, both being entitled "Playback data detecting method", and a method of performing the Viterbi decoding by subjecting the recorded code having the minimum non-inverted interval of 3-channel bits to the ternary detection and a method of performing the Viterbi decoding by subjecting the recorded code having a minimum non-inverted interval of 3-channel bits to the binary detection are described in the Japanese Unexamined Patent Publication Nos. 4-307817(1992) and 6-124549(194), respectively, both being entitled "Playback data detecting method". The detailed description thereof is omitted here.
Moreover, optimal equalization by way of automatic adaptation is described in "Digital Signal Processing", edited by the Institute of Electronics, Information and communication Engineers, pp. 240-245.
Multiplying coefficients am1 to am5 can be expressed in the following equations, wherein subscripts t to 2-t indicate time, "sign" indicates a function, .SIGMA. indicates an integrated value, "dx" indicates a predetermined delay value of an input data after binary determination, "dy" indicates a predetermined delay value of an output data after binary determination and ".epsilon." indicates a value obtained by subtracting "dy" from the predetermined delay analog value of an output data.
Equation 1!
MZF method EQU am1.sub.t+1 =am1.sub.t -sign (.SIGMA..epsilon..sub.t-2 .multidot.dx.sub.t) EQU am2.sub.t+1 =am2.sub.t -sign (.SIGMA..epsilon..sub.t-1 .multidot.dx.sub.t) EQU am3.sub.t+1 =am3.sub.t -sign (.SIGMA..epsilon..multidot.dx.sub.t)(1) EQU am4.sub.t+1 =am4.sub.t -sign (.SIGMA..epsilon..sub.t .multidot.dx.sub.t-1) EQU am5.sub.t+1 =am5.sub.t -sign (.SIGMA..epsilon..sub.t .multidot.dx.sub.t-2)
Equation 2!
ZF method EQU am1.sub.t+1 =am1.sub.t -sign (.SIGMA..epsilon..sub.t-2 .multidot.dy.sub.t) EQU am2.sub.t+1 =am2.sub.t -sign (.SIGMA..epsilon..sub.t-1 .multidot.dy.sub.t) EQU am3.sub.t+1 =am3.sub.t -sign (.SIGMA..epsilon..sub.t .multidot.dy.sub.t)(2) EQU am4.sub.t+1 =am4.sub.t -sign (.SIGMA..epsilon..sub.t .multidot.dy.sub.t-1) EQU am5.sub.t+1 =am5.sub.t -sign (.SIGMA..epsilon..sub.t .multidot.dy.sub.t-2)
Although a playback system which performs partial response equalization by way of automatic adaptation in digital disk recorders and digital VTRs which record data by way of recording codes having limited continuous bit length patterns such as the 1-7 code and 2-7 code to obtain data with high reliability after playback, and which further subjects the outputs thereof to bit error correction by way of ternary/binary Viterbi decoding of, 4-state/6-state Viterbi decoding, etc. can obtain data with low bit error rate and high reliability to some extent, the automatic adaptive equalizer and the Viterbi decoder operate independently from each other and are connected to each other in series, so that it cannot be said that such a playback system is optimal from an overall point of view. Accordingly, it is an object of the present invention to reduce the bit error rate of recorded or playback codes so as to detect an optimal playback data by integrally operating the automatic adaptive equalization and Viterbi decoding.